Wheelchair drive units are well known accessories and fall into two distinct categories. The first category is mounted on the wheelchair and drives the tire of one or more wheelchair wheels. The second category, into which the present invention falls, is attached to the wheelchair and has one or more independent drive wheels which rest on and drive against the ground.
It is the action of the drive wheels on the ground which can cause the user problems when they need to negotiate kets or pot holes. While it is known to raise the drive wheel off the ground surface by the use of a cable and lever or screw jack arrangement, these structures and methods are difficult to use or result in minimal ground clearance when actuated.